1. Field of the Invention
The present invention relates to nylon copolymer compositions and to multilayered film structures made therefrom. More particularly, the invention pertains to coextruded films having at least one polyamide copolymer layer attached to at least one olefin containing polymer layer by means of an optional adhesive composition therebetween. Such structures are suitable for use as barrier films, such as aroma barrier films, which have reduced curl. The nylon compositions are extremely uniform, and have only a single melting point rather than individual melting points of the component nylon copolymer parts.
2. Description of the Prior Art
It is known in the art to prepare blends of nylon polymers. Melt blending of N6 and N66 under commercial processing conditions leads to non-homogenous products with two separate phases as indicated by their individual characteristic melting points. It is well known to prepare copolymers of N6 with other polyamides such as nylon 66, nylon 11, nylon 12, nylon 6T, nylon 46, etc. It has now been unexpectedly found that when blends are formed from two different nylon copolymers, each containing either nylon 6 or nylon 66, in certain proportions, that homogenous, super-miscible blends are formed having improved properties. Films produced from dual nylon copolymer compositions, when attached to polyolefin films produce multilayered structures having unexpectedly reduced curl.
U.S. Pat. No. 5,206,309 teaches heat stable films based on melt blends of N6 and N6/N66. U.S. Pat. Nos. 5,053,259 and 5,344,679 teach blends of an amorphous nylon, a copolyamide, and optionally a polyamide homopolymer. U.S. Pat. No. 4,877,684 claims films based on mixtures of nylon 6 and N6/N66. EP Patent 408,390 discloses the use of any polyamide, any copolyamide, or a mixture of polyamides along with amorphous polyamide or a copolyamide. Japanese patent 115,4752 discloses films based on mixtures of an aliphatic polyamide and a partially aromatic amorphous polyamide along with EVOH. AU Patent 8825700 discloses an aliphatic polyamide, e.g., nylon 6 or N6/66 copolymer and an amorphous polyamide. All of these do not teach random copolymers of nylons in certain proportions to form a homogenous, miscible phase composition according to the invention. U.S. Pat. Nos. 4,647,483; 4,665,135 and 4,683,170, show blends of N6 plus a copolymer of N6/N66 or N6/N 12 rich in N6. A film that is formed from a blend of a polyamide and a polyolefin is described in U.S. Pat. No. 4,444,829.
It would be desirable to provide super-miscible blends of semi-crystalline nylon copolymers where each have a nylon 6 or nylon 66 moiety.